The main part of this thesis treats measurements in the HELIOS experiment of the production of e-mu and mu+mu-pairs in 450 GeV/c p-Be collisions. The mumu measurement covers the kinematical covers the kinematical range of 2Mmu < M < 1.5 GeV, 0.03 < xF < 0.25, and 0 < pT < 2 GeV. Production of the vector mesons rho, omega , and phi is observed. The branching ratio omega to mu+mu- is for the first time experimentally measured. The continuum at masses below the mu mass is studied, and compared with the contributions from known sources, normalized to the vector meson peaks in the mu+mu- mass spectrum, and to measurements in this experiment of the mu cross section. The res ult is compared with that of other experiments, discussed in terms of different background estimates used. A significant signal of unlike-sign e-mu-pairs is observed, forming a continuum peaking at a mass below 500 MeV. Correlations between e-mu and neutrino production are studied. The shape of the e-mu mass and missng-energy spectra indicate significant non-charm contributions. A search for lepton-number-violating decays is made, resulting in upper limits on a number of branching ratios. Also discussed here is the author's work in the DELPHI experiment, contributions that are related to analysis of heavy quark production. Keywords: muon. pair, dimuon, dilepton, lepton, low mass, continuum, eta, rho, omega, branching ratio, emu, e-mu, mue, mu-e, muon-electron, electron-muon, electron, charm, neutrino, missing energy